In the absence of curative medical therapy or vaccines to prevent Human Immunodeficiency Virus (HIV) infections, behavioral change, including condom use has been promoted for reducing the risk of sexually transmitted HIV acquisition. Although the potential benefits of condom use appear self-evident, many individuals at risk for HIV fail to use them. Recent considerations have resulted in appreciation of a number of additional shortfalls in current understanding of condom use. The objective of this project is to examine the use of condoms to prevent acquisition of STDs including HIV in both a high-risk and a community- based population in Baltimore. The specific aims of the proposed study are: 1. To describe the prevalence of condom use and the characteristics of condom users, as compared to those who do not use condoms in studies of high risk patients ages 14-35 attending Baltimore STD clinics and in a community-based sample of Baltimore residents ages 14-35 years; 2. To develop more accurate measures of self-reported condom use behavior, validating these measures by detection of incident STDs; 3. To analyze determinants of condom use to prevent STDs in STD clinic patients and in city residents, and of changes in condom use over time in the clinic population; 4. To compare condom use in STD clinic patients infected with an STD closely linked to HIV risk (syphilis) to condom use in patients with other STDs. The conceptual framework and hypotheses for this project are based on a modified Health Belief Model adapted to the problem of condom use. The STD clinic study design will utilize rolling enrollment of 2,250 clients over three years, evaluated with baseline interviews and a followed-up at 6 months to monitor behavior change and to validate self-reported condom use by detection of incident infections. The community-based surveys will be conducted in two waves, two years, apart using an instrument incorporating the same questions as the STD clinic study, using telephone and face-to-face interviews in a 3:1 ratio. The project will result in two data sets which will be analyzed separately and in integrated fashion. this project will contribute needed knowledge on condom use which will be important for design of interventions for condom use to prevent HIV infections in both high-risk and general populations.